与JSTL中的枚举值相比 [英] Comparing with enum value in JSTL
问题描述
public static enum CountryCodes实现EnumConstant {
USA ,CAN,AUS;}
在jsp中,我试图遍历枚举值并执行比较:
< c:set var =countryCodesvalue =<%= RequestConstants.CountryCodes.values )%>中/>
< td>< select>
< c:forEach items =$ {countryCodes}var =countryCode>
< c:choose>
< c:当test =$ {CURRENT_INSTITUTION.countryCode == countryCode}>
< option value =$ {countryCode}selected =selected> $ {countryCode}< / option>
< / c:当>
< c:否则>
< option value =$ {countryCode}> $ {countryCode}< / option>
< / c:否则>
< / c:choose>
< / c:forEach>
< / select>< / td>
但是,问题是, CURRENT_INSTITUTION.countryCode
从数据库读取,可能不是枚举值之一。
如果 CURRENT_INSTITUTION.countryCode
是除枚举值之外的值(说 CHN
),则比较会引发以下异常:
java.lang.IllegalArgumentException:no enum const CountryCodes。 CHN定义。
我必须应对这种情况,因为数据库存储旧的数据,这是不健全的,可能包含无效值。
所以有一种比较方法,当 CURRENT_INSTITUTION.countryCode
不是枚举之一时返回false值?或者有没有办法确定 CURRENT_INSTITUION.countryCode
是否是枚举值之一,以便我可以采取适当的措施?
在返回名称的枚举中定义一个getter:
public String getName(){
return name();
}
然后你可以比较字符串。
如果您的EL版本支持方法调用,可以跳过getter并使用 countryCode.name()
I have the follwoing enum in my backend java code:
public static enum CountryCodes implements EnumConstant {
USA, CAN, AUS;}
And in the jsp I am trying to iterate through the enum value and do an comparison:
<c:set var="countryCodes" value="<%=RequestConstants.CountryCodes.values()%>" />
<td><select>
<c:forEach items="${countryCodes}" var="countryCode">
<c:choose>
<c:when test="${CURRENT_INSTITUTION.countryCode == countryCode}">
<option value="${countryCode}" selected="selected">${countryCode}</option>
</c:when>
<c:otherwise>
<option value="${countryCode}">${countryCode}</option>
</c:otherwise>
</c:choose>
</c:forEach>
</select></td>
However, the problem is that, CURRENT_INSTITUTION.countryCode
is read from database and might not be one of the enum value.
If the CURRENT_INSTITUTION.countryCode
is value other than the enum value, (say CHN
), then the comparison throws the following exception:
java.lang.IllegalArgumentException: no enum const CountryCodes.CHN defined.
I have to cope with this situation because the database stores old data, which is not sanity-checked and may contain invalid value.
So is there a way for the comparison to just return false when CURRENT_INSTITUTION.countryCode
is not one of the enum value? Or is there a way to determine whether CURRENT_INSTITUION.countryCode
is one of the enum value or not, so that I can take proper action based on that?
Define a getter in the enum that returns the name:
public String getName() {
return name();
}
Then you can compare strings.
If your EL version supports method calls, you can skip the getter and use countryCode.name()
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